Materials Research to Meet 21st-Century Defense Needs (2003) / Chapter Skim
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6 Functional Organic and Hybrid Materials
6 Functional Organic and Hybrid Materials
Pages 135-180
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From page 135... ...
The panel has identified a number of research opportunities, among them: · Promotion of the convergence and integration of organic and Si electronics and other semiconductor and photonics into hybrid architectures; · New synthetic strategies to produce high yields of selected polymers with completely defined chemical structures and with enhanced homogeneity and purity; · Computer modeling and simulation, accessible to experimentalists, to optimize chemical and structure selection for specific functionalities (organic materials, especially macromolecular, that display high photovoltaic and thermoelectric figures of merit are particularly valuable for military applications)
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From page 136... ...
· Combinations of low- and high-molar-mass organic molecules with inorganic materials will become widespread, offering unique functional advantages. INTRODUCTION The Panel on Functional and Organic Hybrid Materials believes that organic materials of low or high molar mass are destined to play a vastly increased role throughout the entire spectrum of military applications for the foreseeable future.
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From page 137... ...
mi I itary. DOD NEEDS FOR FUNCTIONAL ORGANIC AND HYBRID MATERIALS Electronic Devices The military will always have a need for low-cost expendable and long-term durable electronic devices.
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From page 138... ...
Quantum effects associated with nanometer size dimensions are already considered in the design of microelectronic devices. Thus, it is possible that all organic molecular electronics will find either a significant niche apart from conventional CMOS systems or that hybrid products will be created using both technologies (Seabaugh and Mazumder, 19991.
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From page 139... ...
If such optical limiting materials can be synthesized, their impact on soldier protection wi l l be enormous. Organic Light-Emitting Materials Low-cost, addressable, lightweight, full-color displays on flexible organic substrates with efficiencies in the 50-100 lumen/watt range or higher have substantial implications for information dispersion at the soldier level.
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From page 140... ...
Photorefractive Materials The photorefractive effect has long been recognized to possess great potential for military applications (Gunter and Huignard, 1998; Solymar et al., 1996) , including high-capacity optical memories, dynamic hologram formations, massive interconnections, high-speed tunable fi Iters, phase conjugation, real-time handling of large quantities of information, and realtime relay lines for phase-array antenna processing.
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From page 141... ...
Metal Organic Catalysts The principal areas important to metal organic catalysts for future materials for defense are smart materials, fuel conversion, and self-healing structures. In the case of smart materials, embedded catalysts are expected to act through a feedback loop as both sensors and actuators; an example is a metal organic that senses a biohazard and actuates a catalytic antidote.
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From page 142... ...
Electronic Devices The basic components needed to create electronic devices on a molecular scale are wires, switches, rectifiers, and transistors. Molecular Wires An organic solid [tetrathiafulvalene (TTF)
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From page 143... ...
Switches A simple molecular switch allows transport of electrons through a molecule while at the same time being able to disrupt the transport process in the molecule via conformational changes or other reversible reactions. For example, photochromic molecules can undergo a photo-induced intramolecular change in their molecular orbital structure that can favor or reduce electron transfer, depending upon the final molecular configuration R1 s 1 R2 FIGURE 6-2 n = 6-1 8 Potential molecular wire material that takes advantage of c, bonds in polyorganosilane materials.
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From page 144... ...
Organic molecules that can be electronically switched on or off for extended periods might be used as the basic components of memory and logic devices. The molecules of choice are highly conjugated donor/ acceptor functionalized phenylene ethynylene oligomers that are very sensitive to their local environments.
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. Electronic Circuits It has now been established that most, if not all, of the individual basic molecular-scale building blocks that are required to create electronic circuits have been demonstrated.
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. Alternative technologies like carbon nanotubes or molecular electronics vying to replace silicon technology for computing and data storage must meet certain criteria, such as high levels of integration (>109 transistors/circuit)
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If molecular electronics is to provide a solution, partial or otherwise, for miniaturization of electronic devices, a number of major research and development hurdles must be cleared before high-performance, economic, and reliable devices can be produced at the molecular scale. One of the first challenges for circuits composed of molecular wires, rectifiers, transistors, and so on is fabrication or assembly and connection of all the individual components.
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From page 148... ...
Fabrication of single molecules between electrodes Maintaining molecular contact between electrodes during military operations Long-term durability of the electrical conductivity or resistance of the organic molecule Voltage recycle capabilities over extended periods Maintaining alignment of the film structure over time Control of the switch (limiting switching errors at the molecular level) Reversibility of the switch Readability at the molecular level Input/output attachments (nanowires or optical circuits)
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From page 149... ...
, electroluminescent phosphors, and even miniature halogen or metal halide arc lamps are widely used today in telecommunications, sensor products medical diagnostic applications, optical circuits, equipment inspection, and optical recording/reading devices. There is a major effort to commercialize organic LEDs for display applications.
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From page 150... ...
High-speed, organic polymer-based, optical intensity modulators or switches operate on the principle of second-order molecular optical nonlinearity, or nonlinear polarization of highly unsaturated and aromatic 150
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From page 151... ...
have improved their light transmission properties. Polymer optical fibers may never Electron Donor FIGURE 6-7 Highly Conjugated Electron Bridge Electron Acceptor Basic structures of electro-optic chromophores.
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) are created using sophisticated integrated silicon-based optical circuits.
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From page 153... ...
The advantage of these photonic bandgap materials is that they can control light in fully integrated optical circuits and thus become a basic foundation or building block for an optical computer (Levi, 19991. it Although the early work in photonic bandgap material is based on norganic waveguide materials, it is possible to develop periodic dielectric structures based on incompatible blends of polymers.
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From page 154... ...
This final information packet might be used to activate another system as a final output of the analysis (Figure 6-91. Table 6-2 contains a summary of where organic and polymeric materials need to be developed to create photonic devices that will have advantages over other technologies and meet military application needs in the future.
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From page 156... ...
Lightweight Not sensitive to electromagnetic interference High sensitivity at low cost Radiation resistant Low dispersion in the index of refraction between I R a n d m i l l i m eter-wave frequencies Easy to fabricate Low power consumption Photonic bandgap Optical computers Rapid computational processing speeds materials, Optical data storage Able to process and analyze very large photorefractive banks of diverse data polymers Optical Limiting Materials Optical switches and optical limiters both use nonlinear optical (NLO) effects; the difference between the systems is illustrated in Figure 6-10.
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From page 157... ...
Excited state absorption and free charge carrier absorption are accumulative nonlinear optical processes that require absorption and dissipation of light energy, and that can also be applied to optical limiting. The past several decades have seen studies of various optical limiting materials, such as inorganic semiconductor materials, organ ic or organometal I ic molecu les, fu I lerenes, and nanometer semiconductor or metallic clusters (Tuft and Boggess, 1993; Spangler, 1999; Perry, 19971.
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From page 158... ...
Organic LEDs using both low molecular weight and polymeric lumiphores are now in full-scale production in the United States, Japan, and Europe. These are typically monochromatic displays, though full-color versions are on the immediate horizon, with applications in mobile telephone and small-scale (e.g.
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From page 159... ...
The best candidates for high-temperature ferromagnetic materials are those containing magnetic transition metal ions. Purely organic ferromagnetic materials are difficult to prepare and the several reported systems are controversial.
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From page 160... ...
Depending on the nature of the metal ions, a wide range of Tc is observed [Tc = 75 K, M = Mn''; Tc = 75 K, M = Fe''; Tc = 350 K, M = V''l. Materials based on fullerenes and their derivatives are of interest.
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From page 161... ...
Molecular Magnetic Materials: Summary Molecular magnetic materials can be expected to offer a range of properties that can be tuned by design and implemented by the methodology of synthetic chemistry. These tunable properties will include controlled mass density, mechanical flexibility, low-temperature processibility, high strength, solubility, low environmental contamination, compatibility with polymers for composites, biocompatibi I ity, h igh magnetic susceptibi I ities, .
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From page 162... ...
The advances in molecular engineering have produced numerous polymeric and molecular PR materials and three fundamentally different strategies for preparing PR polymers and organic materials: composite polymeric materials, fully functionalized polymers, and monolithic molecular materials. Composite materials consist of polymer hosts (EC)
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From page 163... ...
A second option is fully functionalized polymers that contain all of the necessary functions for the PR effect in a single polymer chain (Wang et al., 20001. Different functional polymers have been reported to exhibit PR effects, including functional polyurethanes, functional conjugated polymers, functional polyimides, and conjugated polymers containing transition metal complexes.
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From page 164... ...
Organic materials, either as low-molar-mass compounds on a flexible support or as polymers, are attractive because typically they offer the prospects of facile, large-area fabrication, mechanical flexibility, much lower cost, and fine-tuning of optical properties to match the absorption characteristics of the solar spectrum. To date, many limitations of organic materials have been recognized, and much fundamental research is still needed to address them.
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From page 165... ...
The self-assembly of liquid crystals is a promising approach, and there are opportunities for simultaneous synthesis and processing of organic-based photovoltaic devices. Toward that end, one proposal is to prepare stretch-oriented, conjugated polymer films with conductive polymer-dipolar-molecular materials acting as antennae and diodes to convert light to electric power (Marks, 19931.
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From page 166... ...
Applications include membrane-based separations (e.g., desalination of water by reverse osmosis) that represent an important class of operations in the chemical industry, ion-transporting films as solid electrolytes in power sources and organic LED devices, and protective clothing for combat personnel.
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From page 167... ...
As an example, in new proton-conducting block copolymer membranes for fuel cells, nanoscopic conducting domains spontaneously organize during processing. Block copolymers are also being considered as protective membranes for soldiers that can be selective about absorbing toxic agents yet be breathable for comfort due to the dual roles of the compositionally different, phase-separated domai ns.
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From page 168... ...
Attention should also be given to membranes capable of cleaning water with minimal energy expenditure, and to iontransporting membranes for high-performance power generation (Koros et al., 1 9921. Metal Organic Catalysts A catalyst is a material that promotes a chemical reaction without becoming part of the product.
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From page 169... ...
Metal organic catalysts work on C-H, C-C, and C-F bonds. Homogeneous catalysts should be studied in a step-by-step process to gain a mechanistic understanding of complexation, oxidative additions, reductive elimination, and insertion/migration mechanisms.
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From page 170... ...
The perceived benefits of these hybrid organic-inorganic materials in the context of metal organic catalysts are that an inorganic matrix (1 ) improves thermal stability, (2)
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From page 171... ...
RESEARCH AND DEVELOPMENT PRIORITIES In this chapter, the panel outlines its assessment of the opportunities that functional and organic hybrid materials offer for revolutionary new military capabilities by 2020. From this analysis, the panel has extracted five broad R&D priorities, discussed below, that are considered critical to the realization of these opportunities.
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From page 172... ...
Major issues will need to be addressed, such as how to match sometimes disparate properties like thermal expansion and optical absorption. New Synthetic Strategies to Produce High Yields of Selected Polymers with Completely Defined Chemical Structures, Enhanced Homogeneity, and Purity Synthesis and processing today are typically separate operations.
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From page 173... ...
However, there will be an increasing push to exploit the properties of individual molecules, or very small aggregates of molecules, for the next generation of electronic and optical devices. For example, carbon nanotubes and collections of only a few organic molecules are being studied as components of diodes, transistors, and memory elements.
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From page 174... ...
Catalyst Systems to Provide in Situ Defenses by Neutralizing Chemical and Biological Attack Metal organic catalysts have a role to play in making materials multifunctional in the true sense of "smart" materials. In case of chemical or biological attack, embedded catalysts are expected to act as both sensors and actuators through a feedback loop.
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1 999. Carbon nanotubes as molecular quantum wires.
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From page 176... ...
2001. Molecular electronics.
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1998. Carbon nanotube based molecular electronic devices.
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From page 178... ...
1990. Molecular electronics.
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From page 179... ...
1992. Polymer optical fibers in data communications and sensor applications.
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From page 180... ...
2001. Photorefractive effect in polymeric and molecular materials.
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